The present invention relates to a bladder handling apparatus for a tire vulcanizing machine and more particularly to an improved bladder handling apparatus which ensures a correct upper positional limit for an upper bladder holding unit without danger of causing injury or damage to a seal member fitted onto an actuating cylinder.
As is well known, a green tire is vulcanized with the aid of a bladder made of rubber in a tire vulcanizing machine, the bladder being included in the green tire during vulcanization. A conventional bladder handling apparatus of the type which is constructed such that both upper and lower bladder handling units are adapted to move upward and downward while the upper bladder holding unit is guided by means of a center post and the lower bladder holding unit is guided within a base for the tire vulcanizing machine is disclosed in Japanese Laid-Open Patent NO. 37518/77 and is widely put to practical use.
FIGS. 1 and 2 illustrate the above conventional bladder handling apparatus. In the drawings, reference letter a designates a bladder made of rubber, reference letter b an upper bladder holding unit, reference letter c a center post, reference letter d a center post actuating cylinder and reference letter e a lower bladder holding unit. The latter unit is firmly mounted on the center post actuating cylinder d. Further, reference letter f designates a guide cylinder for guiding the lower bladder holding unit e, reference letter g a lower die half, reference letter h an upper die half, reference letter i does a lower dome, reference letter j an upper dome, reference letter k a green tire to be vulcanized, reference letter l a hydraulic actuating cylinder, reference letter m a piping through which thermal energy carrier for vulcanization flows, reference letter n a ball nose and reference letter p a loader shoe.
Prior to vulcanizing a green tire the hydraulic cylinder 1 is actuated so as to raise up the center post actuating cylinder d from the lowered position as illustrated in FIG. 1 to the elevated one in FIG. 2 and the latter is then actuated so as to allow the center post c to be extended. The green tire k to be vulcanized is previously disposed in the position as illustrated in FIG. 2 by means of the loader shoe p. Then, the bladder a is located opposite to the inner wall of the green tire k.
Next, a thermal energy carrier such as steam or the like is introduced into the bladder a by way of the piping m until the bladder a is expanded to such an extent as illustrated in the left half of FIG. 2. At this moment the upper bladder holding unit b engages the ball nose n. The loader shoe p of the loading apparatus is then disengaged from the green tire k and it is displaced to a position outside the bladder handling apparatus. Next, the upper die half h is tightly placed on the lower die half g in correct alignment with the latter and the thermal energy carrier is then introduced into the bladder a and both the upper and lower domes j and i while the domes are joined to one another in a gas tight manner, until the intended vulcanization is effected for the green tire k.
As described above, the conventional bladder handling apparatus is constructed such that while the upper die half is raised up steam is introduced into the bladder so as to expand the latter and carry out a preliminary forming process for the tire with the upper bladder holding unit raised up to the elevated position. Obviously, the upper positional limit of the upper bladder holding unit can be correctly controlled when a hydraulic cylinder is employed for the center post actuating cylinder d but it has been found that maintenance service is practiced only with much difficulty. For the purpose of effecting easy maintenance a pneumatic cylinder is employed for the conventional bladder handling apparatus. Accordingly, it has a drawback in that a higher steam pressure cannot be utilized because of free movement of the upper bladder holding unit caused by the resiliency of the pneumatic cylinder.
To obviate the above drawback there was proposed a modified bladder handling apparatus as illustrated in FIG. 3 which includes spacers a' and b' adapted to define the upper positional limit of the upper bladder holding unit during the expansion of the bladder f', the spacer b' allowing the upper chamber of the center post actuating cylinder c' to be in communication with the interior of the bladder f' therethrough. However, it has been found that there is a drawback of shortened running life of the seal member d' due to the arrangement that it is exposed directly to a high temperature thermal energy carrier in the bladder f'. It should be noted that in FIG. 3 reference letter e' designates an upper bladder holding member.